In electrolytic refining of copper, copper and arsenic gradually accumulate in the electrolytic solution. For this reason, a part of the electrolytic solution is extracted and subjected to an electrolyte purification. At the time of this electrolyte purification, a copper-arsenide-containing slime (Cu3As and the like) is extracted. The copper-arsenide-containing slime generally contains 40 to 60 mass % of copper, 20 to 40 mass % of arsenic, and 0.5 to 5 mass % of each of lead, tin, antimony, bismuth and the like. Therefore, after impurities such as arsenic are removed, the copper-arsenide-containing slime is returned to the copper smelting step and then the copper is recovered from the copper-arsenide-containing slime. Meanwhile, impurities such as arsenic are gradually accumulated in the copper smelting and refinery system and adversely influence on the copper quality, thus these impurities are to be removed outside the copper smelting and refinery system.
As a method for immobilizing arsenic, in which the arsenic contained in the copper-arsenide-containing slime or the like is incorporated into a stable compound and the arsenic is removed outside the copper smelting system, for example, the following treatment methods are conventionally known.
In the method disclosed in Patent Document 1, at first, a sodium hydroxide solution is added to a copper-arsenic-containing substance (substance containing copper and arsenic). The mixture is heated while the air is blown into the mixture; and thereby, alkaline oxidizing leaching is carried out. After the leaching is finished, a pH value of the treated solution is adjusted to 7.5 to 10. The treated solution is subjected to a solid-liquid separation to be separated into a leach residue containing copper and a solution containing arsenic. Next, a ferric compound is added to the solution containing arsenic so that a Fe/As molar ratio is in a range of 0.9 to 1.1, and thereby, a FeAs precipitate is formed. The FeAs precipitate recovered by solid-liquid separation is mixed with a sulfuric acid solution to prepare an acidic slurry or acidic solution. Next, the slurry or the solution is subjected to a heat treatment to form crystalline scorodite (FeAsO4.2H2O), and thereby, the arsenic is immobilized.
In the method disclosed in Patent Document 2, at first, arsenic-containing smoke ash (dust) is leached with water under heating to extract arsenous acid (As2O3). Next, an oxidizing agent (manganese peroxide and the like) and calcium hydroxide (slaked lime) are added to a filtrate and reacted mutually. As a result, calcium arsenate is produced and recovered. Next, calcium arsenate is mixed with recycled glass powder, and the mixture is melted at 1200° C. to produce an arsenic-containing glass solidified body.
In the method disclosed in Patent Document 3, first, a sodium-based alkaline residue containing arsenic and antimony is heated at a temperature of 850° C. to 1200° C., and antimony is selectively reduced and separated by a carbon-based reducing agent. Next, a glass component is added to residual sodium arsenate, and the mixture is heated and melted to produce a glass solidified body of the arsenic.
According to the method described in Non-Patent Document 1, a CaO—SiO2-based slag and calcium arsenate are heated and melted at 1400° C. under a constant oxygen partial pressure to produce a glass solidified body of the arsenic.